The overall objective of this research is to investigate the neural control of ACTH and GH secretion in the rat. With regard to ACTH secretion, one series of studies will attempt to further localize, using serial blood sampling and various ablative techniques, the structures essential for circadian rhythmicity and to determine their roles in other periodic functions. Other experiments will study the structures and mechanisms involved in stress-induced activation of the pituitary-adrenal axis. Attention will be focused on the role of the limbic system in response to "psychic" stimuli. Several experiments will deal with the structures responsible for the persistence of stress responses following surgical isolation of the hypothalamus. Another aim is to investigate rapid and delayed feedback control of ACTH secretion and their sites of action. Plasma corticosterone levels, measured fluorometrically, will be used as an index of ACTH secretion in most experiments. A radioimmunoassay (RIA) for ACTH will be established and used in some studies. Several projects will deal with the control of GH secretion and growth. Some of these will study the role of the preoptic-anterior hypothalamic area (PO-AHA) in inhibiting nonstress GH secretion and in mediating stress-induced suppression of GH secretion. A major effort will be made to determine the effects of midline PO-AHA lesions which cause elevated GH levels and blockade of stress responses on hypothalamic somatostatin levels. A final series of experiments will explore the factors responsible for increased linear growth after hypothalamic surgery. GH levels will be measured by RIA and somatostatin by RIA and bioassay.